Investigators were now able to enter the site and would be active through the day, a spokesman said. There was little likelihood that the cause of the blast would be discovered immediately, he added.

Two workers died when solvents exploded on Tuesday morning at a tank depot in a plant operated by the Currenta company and 31 were injured. Five remain missing and are presumed to have died.

Police were accompanied by the environmental authorities, company experts and criminal investigators. Drones will also be used.

A  negligent homicide investigation was opened into the explosion on Wednesday.

Police said they were doubtful whether all parts of the plant could be entered, as there was danger of structural collapse and contamination with toxic chemicals.